MEMS devices are micro-machined devices or systems, generally of a micron or nanometer size and incorporating integrated micro-sized sensors, actuators, signal processors, control circuitry and other like components. Thanks to their small size, lightweight, low power consumption, low price, reliable performance and other advantages, MEMS devices have found extensive use in a variety of applications.
MEMS is a new high-end technology emerging in recent years and developing rapidly. Based on advanced semiconductor fabrication technology, MEMS devices can be massively produced with well-controlled production costs and high product consistency. Typical fabrication process of MEMS devices is a micromachining process that involves film deposition, photolithography, epitaxy, oxidation, diffusion, injection, sputtering, evaporation, etching, dicing, packaging and other necessary steps for fabricating complex three-dimensional structures. In these steps, film deposition, photolithography and etching are most critical for the fabrication process of MEMS devices.
FIG. 1 shows a conventional MEMS device, generally designated by the numeral 10. MEMS device 10 includes a substrate 11, a nickel-iron (NiFe) layer 12 formed on the substrate 11, a tantalum nitride (TaN) layer 13 formed on the NiFe layer 12 and a trench 14 formed in the TaN layer 13.
Principal steps of forming the MEMS device 10 include: providing the substrate 11 and successively forming thereon the NiFe layer 12 and TaN layer 13; and coating a photoresist on the TaN layer 13 and performing photolithographic and etching processes to form the trench 14 in the TaN layer 13. Obviously, the photoresist acts as an etching mask herein for the TaN layer 13 during the formation of trench 14.
However, etching of the TaN layer 13 tends to generate a great amount of polymeric substances which will react with the photoresist disposed on the surface of the TaN layer 13 and hence yields tantalum-containing polymeric products in a large amount. Such resulting polymeric substances contain, in addition to tantalum, carbon, hydrogen and other elements that are hard to be removed and will remain as a deposit in the formed trench. This will reshape the vertical walls of the trench 14 into sloped surfaces. As shown in FIG. 1, the opposing side faces of the remainders of the etched TaN layer 13, which form the walls of the trench 14, are both inclined at an angle (a) of generally 50° to 60° with respect to the respective bottoms thereof. Such sloped walls require the trench 14 to have a larger width at the top edges, which is detrimental to the performance of the MEMS device being fabricated.
Therefore, there is an urgent need in this art for a solution to address the performance degradation of the conventional MEMS device caused by the residues of tantalum-containing polymeric substances generated during the etching process for the TaN layer.